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' Ururnn STATES ATENT Fries.

LUDWIG GRAEAU, oFHANov ER, PRUSSIA, GERMANY.

SPECIFICATION forming part of Letters Patent No. 386,704, dated July 24, 1888.

Application filed June .38, 1887. Serial No.2l2'789.

June 1.], 1887, No. 179,219 No. 23,116.

(Specimens) Patented in Belgium June 11, 18El7,No.77.780; in France in England October St, 1887. No. 14,356, and in Austrizefi'ungary December 2, 1837, No. 49.008 and To all whom it may concern.-

Be it known that I, LUDWIG GRABAU, en-

. gineer, asubject of the King of Prussia, resid- Batentin Belgium, "175789; in Austria-Hu Io.

ant to which it appertains to make and use the e This-invention relates to the separation of the-aluminium fluoride from cryolite (Ahhl GNaF) and to the simultaneous conversion into aluminium fluoride of the alkali fluoride v minium fluoride by means of a aluminium fluoride.

combined with the aluminium fluoride; and .it consists in the processsubstantially as hereinafter described, and set forth in the claim.

In the production of aluminium from alumetal of the ulkalies the proportions are so chosen that th ypro ct btaiued besidcs the aluminium will hfave the. composition of cryolite. The useof t'hiscryolitc by-product is ofgreat advantage in the manufacture or production of aluminium from aluminium fluoride,in that the aluminium fluoride is isolated or separated therefrom and lhesodium fluoride of the cryolite is at the same time converted into So far as 1 am aware, no

practical -process has been known before" my invention whereby this end is attained.

.fectcd by latter may.

According to my invention, the separation or isolation of the aluminium fluoride and the simultaneous conversion of the alkali fluoride in the cry lite into aluminium fluoride are effile-ans of sulphate of-alumina. 'The be'eniployed as such or in combialum or sulphate of alum nium nation as;

essentially by thefollowing two methods. v First. A solution of-sulphate of aluminium spar and'lieatcd to about 90 will be equal in volume to the aluminium sulphate free from water contained in the solution. The conversion or reaction will take place according to the following formula:

The clearsoand the alkali sulphate finally renioved by Washing in water.

Second. To effect asaving of cryolite-that is to say, in order to obtain a maximum quantity of aluminium fluoride from a minimum quantity of cryolite tnc sulphate of aluniiir v I ium solution may first be treated with fluorspar in order to convert the major portion of the aluminium sulphate into a fluoride. "0 this end I employ a solution which contains about ten per centum of'aluminium sulphate, Al,(SO,),, and it is immaterial whether the solution contains aluminium sulphate only ora solution containing both the sulphate and a salt of the alkalics. This solution is treated with an equivalent volume of pulverized fluorconversion or reaction a to the following formula: Al,(SO,),+3(CaFl,) =Al,Fl,,SO,+ 2(CaSO,) CaFl,. According to the duration of the action of the pulverized fluor-spar, the temperature applied, thequa'ntity used, and the composition thereof, from two-thirds to three-fourths of the volume of aluminium sulphate .is converted into aluminium fluoride. The solution ofsulphate of aluminium fluoride so obtained is then freed from the gypsum tion and from the undecomposed floor-spar by filtration and compression.

In order to convert the remainder of the aluminium sulphate into aluminium fluoride, the solution of sulphate of aluminium fluoride or alum, is treated with natural or artificial cryolite'iu such'proportions that the cryolite ccntigrade, the taking place accordin produced during the reacis treated wiln eryolite, the reaction taking ide which consists in treating a solution ot' place according to the following formula: aluminium sulphate such as described with 15 sodium or potassium cryolite, evaporating the solution, heating the pro-net to redness, and finally washing the same, s *hstantially as described.

In testimony whereof I atlix my signature in :0 presence of two witnesses.

l LUDWLG GRABAU.

Vt'itnesscs:

E. PIIUJIIWYIHAL, Jon. Knaeun.

From this solution the aluminium fluoride'is obtained substantially as above. describednamely. by evaporation, heating to redmss or igrnitien of the product, and washing out of the alkali sulphate.

Having described my claim is The process of producing almninium tluoi' invention, what I 

